Method for recovering hydrogen halide



Patented l16, 1945 Bernard S. Friedman, Chicago, Ill.. assignor'to.Universal Oil Products Company, Chicago, Ill.,l y a corporation ofDelaware v K Application May 9, 1942, Serial No. 442,357

6 Claims. (Cl. 260683.4).

This invention relates to a method for recovering relatively dryhydrogen halides from gas mixtures containing hydrogen halides and moreparticularly is 'concerned with'the method of recovering and returninghydrogen halides to hydrocarbon conversion processes in which relativelydry hydrogen halides are employedas catalyst activators.

In catalytic processes such as alkylation of hydrocarbons in thepresenceof an aluminum halide catalyst, it is generally necessary to add arelatively small amount of` hydrogen halide to activate the aluminumhalide catalyst. The hy- A' drogen halide is generally not consumed inthe process but is carried out of the reaction zone with the conversionproducts. hydrogen halide that is added is usually from abutl to about10 mol per cent of the total hydrocarbons4 charged to the process, andin order to reduce the operating cost, it is desirable to recover thehydrogen halide from, the conversion products so that itmay be recycled.Thusthe exit gases from, such a process in which isoparains arealkylated with oleflns contain'rethane and/or propane as well as ahydrogen halide such as hydrogen chloride. A hydrogen halide'l such ashydrogen chloride or hydrogen bromide is easily separated byfractionation from hydrocarbons heavier than propane, but it is notseparated easily from ethane or propane. If ethane and propane are notseparated from the hydrogen chloride that isrecycled, an undesirableamountof these hydrocarbons will gra'dually build up withinthe system.'The present invention makes possible the recovery and recycling tofurther use of hydrogen chloride present in the exit gases fromhydrocarbon conversion processes in which it is employed asa catalystactivator. y

In one'speciiic embodiment the present invention comprises a process forrecovering relatively dry hydrogen halide from 'a mixture of hydrogenhalide and hydrocarbon gases which comprises contacting the mixture withan olen under hydrohalogenating conditions to form a product containingan alkyl halide, separating'v said alkyl halide from hydrocarbon gases,decomposing substantially all 'of said alkyl halide to liberatetherefrom hydrogen halide, and vsep-.- aratig the liberated hydrogenhalide from the ide. v A. j In the process of the present invention ahydrogen halide such 4as hydrogen chloride or hyother decompositionproducts of said alkyl hal- The amount of hydrocarbonconversion process,is recovered by contacting said exit gases with an olefin underhydrohalogenating conditions to form a mixture containing an alkylhalide which is readily separable by distillation from the paraflinhydrocarbons present in the 'exit gas. 'I'he alkyl halide so obtainedmay in some cases be recycled to the hydrocarbon conversion oralkylation zone but in other cases it Iis sometimes desirable to decom--pose s'aid alkyl halide either thermally or catalytically to liberatetherefrom the hydrogen halidewhich is then recycled to' the reactionzone,/

such as an alkylation zone.' Decomposition of -an alkyl halide toliberate hydrogen halide therefrom generally results in the simultaneousformation of an oleiin. which can be utilized in an alkylation reactionwithout separation of hydrogen halide therefrom.

One hydrocarbon vconversion process which may-employ this method ofrecovering hydrogenhalide is, by way of illustration, the alkylatiorl ofisobutane with. ethylene, propylene, a

higher olen, or mixtures thereof, in the presence of an aluminumchloride catalyst and hydrogen chloride. Usually theoleiin-containingmixture charged will contain some ethane and propane as well as ethyleneand propylene. These saturated hydrocarbons therefore appear in the exitgases alongwith the hydrogen chloride whichis introduced with the chargeto acti- A vate the catalyst. In order to favor alkylation and toinhibit certain undesirable side reactions including polymerization, itisnecessary to have present a substantial molar excess of isobutane tooleiins lthroughout the entire reaction. The f products withdrawn fromthe alkylation zone'are fractionated into a substantially saturatedgasoline, unconverted isobutane, and a gasmixture containing hydrogenchloride. Said gas mixture is commingled with an olen as ethylene or ahigher olenn and contacted with a hydrohalogenating catalyst such asaluminum chloride, aluminum bromide, ferrie chloride, ferrie bromide,bismuth chloride, boron fluoride, etc., under hydrohalogenatingconditions of tempera-` ture and pressure to form an alkyl halide whichis vreadily separable by'ractional .distillation from the lower boilinghydrocarbons such as `ethane and propane. The alkyl halide is cooled andremoved as a Aliquid which is either charged back to the alkylation'reactor4 or decomposed to e olen and hydrogen chloride by passage' overa drogen bromide present in the exit gases of a catalyst known :topromote dehydrohalogenation such as barium chlorideon pumice or onalumina l taining valve 41V mentioned. The e.

maintained at a temperature to about 550 C. l'

`The-accompanying drawing illustrates diaof from about 350 grammaticallyan aluminum chloride alkylation'l an athene-ethylene fraction.

Referring to the drawing, an isobutane iraction at a desired reactiontemperature is introduced through line I and valve 2 to pump 3 whichdischarges through line 4 and valve 5 to cata-l lyst pick-up chambercontaining granular aluminum'chloride. In line 4 the charged isobutaneis commingled with recycled isobutane directed thereto through line 4Ias hereinafter set forth.

In catalyst pick-up chamber 6 the isobutane charged thereto dissolves aportion of the aluminum chloride catalyst and the resultant solution isdirected from chamber 6 through line I and valve 8. A mixture of anethane-ethylene fraction and enough hydrogen chloride to make up forlosses elsewhere in the system is introduced lthrough line 9 andvalveIlIl to pump or compressor II which discharges through line I2,valve I3 and line 1.to reactor' I4 containing a granular solid packingmaterial such as alumina,

silica, etc. which does not react-adversely with aluminum vchloride andupon which the incomtroduced should contain sui'liclent ethylene toreact with substantially all oi the hydrogen ch1c ride andato convert itInto ethyl chloride which together with unconverted gases is directedfrom reactor 45 through line 43and valve 49 to fractionator i0 orconventional design provided with reboiler coil I. Ethane and alsopropane, if

the latter is present, are discharged from the top of fractionator 'E3through line`52 and valve53,

while materials boiling higher than the desired alkyl halide arewithdrawn through' line 54 and f valve 55. The alkyl halide such asethyl chloride which is separated from lower boiling. and higherboiling'products in fractionator 60 is discharged as vapor through line66 and valve 51 to 'condenser 53 from which the liquefied alkyl` ,halideis vdirected through run-down line 59 and valve 60 to receiver 6Iequipped with convening aluminum chloride catalyst will be deposited.The molar ratio of isobutane to ethylene the stream entering packedreactor I4 is approximately 1:1 although -this ratio may varybetween'aboutml and about 20:1.

The products from packed reactor I4 pass through line l5 and valve I6 toseparator I1 wherein entrainedvaluminum chloride-hydrocarbon complex orsludge is separated and withtional gas release line 62 containing valve6 3. lThe liqueiied alkyl halide is withdrawn from receiver 0I throughline 64 and valve 06 by pump 66 which discharges through line 61containing valve 68. By closing valve 10 in branch line 69 the alkylhalide may be directed from line 61 through valve 68 and recycle line 14containing valve 16 to line 1, already mentioned, through which thecharged reactants and catalyst enter reactor I4. However, it issometimes preferable to keep valve 68 closed and to directv the alkylhalide from line 61 through line 09 and valve 10 intodehydrohalogenation reactor 1I containing a catalyst such asbariumchloride on pumice or alumina-maintained at a temperature lbetween about350 and about 550 C. in order to substantially decompose said alkylhalide into hydrogen halide and olefln. The dchydrohalo'genationproducts containingsaid hydrogen halide and olen are directed fromreactor 1I through "line 12 and valve 13 to recycle line 14 containingdrawn through line I8 and valve I9. The reaction products-then passthrough line 20 and valve 2l to fractionator 22 of conventional designand provided with reboiler coil 23.- The alkylation product o! gasolineboiling range is withdrawn through line 24 and valve 25 to cooling andstorage, not shown, while higher boiling products are discharged throughline 26 and valve.2 'l.

Isobutane lis withdrawn as a. side-cut from 4i'ractionator 22 throughline 28 and valve 29'to 32 'to receiver 33 provided with gas release'line 34 containing valve- 3l. The liquefied isobutane may be. withdrawnfrom receiver 33 through line 36 and valve* 81. At least a.- portion ofthe isobutane being discharged through line 3G is directed therefromthrough line 38 and `valve 39 to pump 40 j which discharges' throughline 4I and valve 42 into line 4. already mentioned.

From the top of fractlonator 22 a mixture comprising essentially ethane'and hydrogen chloride is directed through line 43 and valve 44 toreactor 45 containing a hydrohalogenating catalyst such as aluminumchloride, ferrie chlo-v ride. bismuth chloride, etc., as such orsupported by a carrier such as alumina and maintained at I ahydrohalogenating temperature which is generally not in excess of about250 C. An olenor clelia-containing fraction such as an -ethaneethylenemixture svintroduced by a .pump or e-ethylene mixture lso ln valves'I5-and 16. `In order to assist in the recycling of either alkyl halideor decomposition products of said alkyl halide, it is generallydesirable to direct a portion of the recovered isobutane from line 4I'through line 14 wherein said isobutane is commingled with the alkylchloride or hydrogen chloride-containingv mixture and recycled to line1, already mentioned.

The process of this invention -is also utilizable for recoveringhydrogen bromide. Sometimes oleiins of higher molecular weight thanethylene may be utilized more easily for producing alkyl halides whichmay be separated readily by fractional distillation from thesubstantially saturated hydrocarbons present in gases 'such as thosereleased from. a hydrocarbon conversion process.

- II'he method of this invention is also applicable to the separation ofoleiinic hydrocarbons from `tion from the lower boiling parainichydrocarbons present in the parafnnlolefm mixture undergoing separation.-An alkyl chloride s formed from an olefin and separated from admiredparaf- 'iins is readily convertible into a mixture of oleiins andhydrogen chloride by treatment with a dehy.

halide to recover therefrom a hydrogen halide.

' other suitable means, not shown, to line 46 conand thence to line 43,already' The-following example is introduced to show resultscbtainablejin the operational the process for. recovering and recyclinghydrogen chloride in isoparaiiin' alkylation, although the example isnot presented with the intention of unduly limit? ing the broad scop'eofthe invention. The eluentgas from aprocess in .Which--isobutane isalkylated with ethylene in ,the presence of an aluminum chloridecatalyst, after separation 1 noleeulathe meth-0d which omprisesadding'an olen to saidmixture and reacting the same with the hydrogen'halidercontent of the mixture'to form an alkylhalide; separating thealkylhalide y of alkylate and excess isobutane; contains mole' l .percent of hydrogen chloride and-92.per cent of ethan'e. About-20 mole percent' of an equal molecular mixture of ethylene and ethane is com--mongled vwithv said-Lhydrogen-chloridefethane mixture and the resultantmaterial. is contacted '1f withvaluminum chloridefcatalyst at atemperature of about 130 C'. wlier'eby ethyl chloride is formed fromsubstantiallyall of the hydrogen :hl oric le, contained in said mixture.l After cooling, .ethyl chloride isin the form of a liquid whichis'readily fractionated from the ethan'e, the latter 'being dischargedfrom the process. The ethyl chloride` is.

then commingled with a portion of the recovered isobutane and recycledto'the alkylation stage of the process. I

In another mode of operation the ethyl chloride obtained after coolingthe hydrohalogenationl .products is passed through a reactor containinga composite of barium chloride and alumina maintained at 400 C. wherebythe ethyl chloride'un- "thsformedfrom said paramnpf less than 4 carbonatoms. and supplying the same to thealkylat- .'thealkylationoi iscbutanewith ethylene wherein the isobutane -landra n etha'neeth'ylene v;frza.ctior i' are subjected' totheaction of an alumi num halide and ahydrogen-halide ofl thelmiddle halogens, and Wherein'there is'separatedfromthe conversion products a gaseousmixture containing hydrogen halideand ethane', themethod which comprises adding ethylene to said mixtureand reacting the same with thel hydrogen halide content of thefmixtureto form anethylfhalide,'separat ingsthe'etnyi halide thus formed ,fromthe emana" :fcontent of said mixture' and supplying the same tothe,alkylatingstep." Y r f`3 ,-i;'I he process defined in claim 1further char-l acterized in that said hydrogen halide comprises hydrogenchloride and said aluminum. halide'coini prises 'i aluminum chloride.

dergoes substantially completev conversion into a t mixtureof hydrogenchloride and ethylene', said mixture being suitably recycled to thealkylation stage of the process. V

The-aboveexample indicates a specific process v in which one embodimentof .my inventionfmay be employed. However,v it is not intended that thebroad scope of the invention described in thespeccationshould belimitediby the examplel given.

I claim as my invention:

1. In the alkylation vof an isoparain with 4an -olen in the presenceof'an aluminum halide and a hydrogen halide -of the middle hal'ogens,wherein there is separated from the conversion prodprises -aluminumchloride. Y

4.Theprocess defined in'claim 1 further charV acteri'zed in thatsaidhydrogen halide comprises l hydrogen bromide' and. said aluminum halidecomprises aluminum bromide; 5.- The process defined in claim 2 furthercharacterized in thatj said hydrogen halide. comprises hydrogen chlorideand said aluminum halide comi- -2 fur-tl'ierchar" acterized in that saidhydrogen halide comprises hydrogen bromideand said aluminumv halide com6. The process defined in claim prises alumix'iun'rbromide.,l

